The integration of chalcogenide materials with nanophotonic circuits for recongurable control of light

Abstract

This thesis aims to develop a new conceptual approach for programmable nanophotonic devices, by combining the silicon photonics platform with lowloss phase change materials (PCMs). The approach brings together silicon photonics and phase change technology into a hybrid platform. Digital patterns of pixels are written in the phase change layer using an optical pump laser, which shapes the flow of light by weakly perturbing light transport in the hybrid photonic waveguide. The advantage of this approach is that once set, the phase change materials are self-holding and therefore passive operation would be possible, all at an unparalleled device foot print.
Traditional phase change materials were tested for this application but were found to have an intrinsic absorption loss that prevented their use, as any guiding effects were offset by the lower total transmission. Therefore, in order to achieve the goals set out in this thesis, an entirely new material platform was needed. A large part of the efforts in this project involved the development of a new family of optical phase change materials with ultralow losses. Sb₂Se₃ was selected as the most suitable material and integrated into a range of photonic devices to characterize the optical and electrical properties before finally realizing a reconfigurable wavefront shaper based on an MMI design. With transmission losses of 100 dB/cm for a straight waveguide clad with 25 nm of crystalline Sb₂Se3, this represents the lowest loss PCM available, whilst still maintaining a sizable refractive index shift between the amorphous and crystalline phases of ∆n=0.77.
A reconfigurable router was demonstrated, capable of reversibly switching the output between two waveguides using a pixel pattern of Sb₂Se₃ distributed in a layer above an MMI. The results in this thesis are the first of their kind and clearly demonstrate the viability of the conceptual approach of freeform patterning of the flow of light using an ultralow-loss phase change material. This work is an initial step towards the development of fully programmable low-loss integrated photonic devices, allowing for optical routing within larger circuits to be realized. This will open up the possibility of low loss, on-chip wavefront shaping applications such as mode converters, neuromorphic computing and LiDAR.

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Identifiers

ORCID for Daniel Hewak: orcid.org/0000-0002-2093-5773

ORCID for Otto Muskens: orcid.org/0000-0003-0693-5504

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